Method, computer program and control device for operating a vacuum reservoir situated inside an internal combustion engine

ABSTRACT

Described are a method, a computer program, and a control unit for operating a vacuum reservoir ( 6 ) provided in an internal combustion engine of a motor vehicle for a servo booster or power-assist unit ( 8, 10, 11 ) of the internal combustion engine, which is coupled to an intake manifold ( 1 ) of the internal combustion engine and to an electrical suction pump ( 30 ). The pressure prevailing in the vacuum reservoir ( 6 ) is determined by a computational model in which quantity flows are fed to the vacuum reservoir ( 6 ) when at least one servo unit ( 8, 10, 11 ) is actuated, quantity flows are removed from the vacuum reservoir ( 6 ) when the pressure prevailing in the intake manifold ( 1 ) is lower than the pressure prevailing in the vacuum reservoir ( 6 ), i.e., when the electrical suction pump ( 30 ) is switched on. The total pressure prevailing in the vacuum reservoir ( 6 ) is calculated from the balance of these flow quantities.

BACKGROUND INFORMATION

[0001] The present invention is directed to a method for operating a vacuum reservoir provided in an internal combustion engine, in particular of a motor vehicle, which supplies the auxiliary power, in the form of a vacuum pressure, needed for at least one servo power-assist (one servo booster) unit, and which is acted upon by a vacuum pressure prevailing in an intake manifold of the internal combustion engine and in an, in particular, electrical suction pump, as well as to a device for this purpose.

[0002] In motor vehicles, it is known (DE 31 25 923 C2, DE 44 44 013 A1) that, for the most part, power brake and power steering systems draw their auxiliary power from a vacuum reservoir which is coupled to an intake manifold. This intake manifold is used to supply the internal combustion engine with the air, i.e., the oxygen that is needed for the combustion. In this context, the intake manifold's vacuum pressure is stored temporarily in the vacuum reservoir, which is coupled via a non-return valve to the intake manifold.

[0003] Accordingly, to provide adequate servo power assistance, for example servo braking power, a vacuum pressure must have been present for a long enough time in the intake manifold to ensure the proper vacuum pressure in the vacuum reservoir. In response to low manifold pressure, air flows out of the reservoir into the intake manifold. The thus minimally attainable pressure in the vacuum reservoir corresponds to the prevailing manifold pressure. In response to actuation of the brake, the vacuum reservoir is connected via a valve to an actuator which boosts the braking power. In the process, air flows into the vacuum reservoir, thereby increasing the reservoir pressure.

[0004] In internal combustion engines of the afore-mentioned type, a throttle valve, which is used to adjust the air supplied to the combustion chamber, is also provided in the intake manifold. In conventional internal combustion engines, in particular in the Otto spark-ignition (gas) engine, the throttle valve closes, even when the driver, during braking, removes his/her foot from the accelerator, so that a possibly existing vacuum pressure in the reservoir is retained. Therefore, in these internal combustion engines, it is ensured that the vacuum reservoir is able to supply the vacuum pressure required for the servo power-assisted brake even during a relatively long braking action.

[0005] However, this is not always ensured in newer internal combustion engines having gasoline direction injection (GDI) or electronic throttle control (e-gas). For example, during the process of heating an existing catalytic converter, the throttle valve is open to the point where there is no longer an adequate vacuum pressure in the intake manifold. As a result, the vacuum pressure required for the servo system(s) is no longer able to be made available in the vacuum reservoir.

[0006] In addition, in internal combustion engines having GDI or electronic throttle control (e-gas), the throttle valve is controlled independently of the pedal sensor position, so that the manifold vacuum pressure is restricted in terms of its availability for servo functions.

[0007] Examples of this are operating states where manifold injection is accompanied by retarded ignition timing for catalytic converter heating during warm-up. In these operating states, it is necessary, namely, to compensate for a wanted loss of efficiency by opening the throttle valve. This leads to an increase in the manifold pressure. Stratified operation accompanied by direct injection is a comparable operating state, where, even at a low load, the throttle valve is fully open, so that, as a result, no manifold vacuum pressure is available.

[0008] In this context, it can also happen during vehicle operation at high altitudes, for example during uphill driving, that the difference relative to the ambient pressure no longer suffices for the servo functions.

[0009] The servo power-assisted brake system is especially critical with respect to safety. If adequate vacuum pressure is not provided, then no brake assistance is available, or the desired operating state cannot be run due to safety considerations, thereby leading to deterioration of the exhaust gas or fuel consumption.

[0010] It is, therefore, already known that a remedy is found by designing the throttle opening in such a way that sufficient vacuum pressure is always available. As a result, the throttle opening is not always able to be optimally designed, in terms of the exhaust gas, for example during the catalyst heating. In addition, in GDI (gasoline direct injection) operated vehicles, a vacuum-operated switch is used. If the pressure in the brake booster rises above a threshold value, then the switch is made from stratified operation to homogeneous operation.

[0011] In the internal combustion engine taken as a basis here, the vehicle has a built-in suction pump, which compensates for the lacking pressure differential as soon as the pressure in the intake manifold no longer suffices for evacuating the vacuum reservoir. To keep costs low, the suction pump should be a relatively simple component, which is only put into operation in truly necessary cases. Due to cost considerations, the outlay required to detect a necessary switching on or a possible cut off of the suction pump should likewise be kept as low as possible.

[0012] It is, therefore, the object of the present invention to provide a method as well as a corresponding device, which, without substantial outlay and with the greatest dependability, will enhance the operational reliability of the vacuum reservoir and minimize mechanical and, thus, also cost expenditures, at the same time, achieving a reliable operation of the vacuum reservoir.

[0013] This objective is achieved in the method according to the present invention by feeding quantity flows to the vacuum reservoir, in a computational model, when at least one servo unit is actuated; by removing quantity flows from the vacuum reservoir when the pressure prevailing in the intake manifold is lower than the pressure prevailing in the vacuum reservoir; by removing quantity flows from the vacuum reservoir when the electrical suction pump is switched on; and by determining the pressure prevailing in the vacuum reservoir from the balance of the flow quantities fed to and removed from the vacuum reservoir.

[0014] The underlying concept of the present invention is, thus, to determine, by calculation, the pressure in the vacuum reservoir, and, therefore, also the vacuum pressure in a servo system, for example in the brake booster. In this context, the pressure differential in the vacuum reservoir, i.e., in the reservoir of the servo system, is calculated by a model. From the balance of air-inflow and air-outflow quantities to and from the reservoir volume, this model determines the specific pressure in the reservoir.

[0015] The compressibility of the gas in the reservoir may be considered in a state equation for ideal gases. The flow quantity into the reservoir may preferably be calculated from the difference between the reservoir pressure and the intake manifold pressure and between the reservoir pressure and the minimal suction pump pressure, allowing for the resistances to flow in the lines to the reservoir. Flow quantities flowing out of the reservoir may be determined from the driving states, e.g., cornering, with the power steering system being loaded to this effect, or a vehicle deceleration, with the power brake system being loaded to this effect.

[0016] In known internal combustion engines, the output variables underlying the concept of the present invention are already known from such a motor control, for example from the “Motronic” motor control system of the applicant. In anti-lock braking systems (ABS), for example, motor control interfaces are already present which transmit information on the air consumption in the servo brake to the engine management. Information on intake manifold pressure, ambient pressure, change in vehicle speed, and the operating state of the suction pump is also usually available in known engine management systems. The additionally required sensors, such as pressure switches or pressure boost sensors in the pressure reservoir (accumulator), are likewise present in existing systems. Thus, in an implementation of the method according to the present invention, no additional construction measures are necessary in existing internal combustion engines. In accordance with one preferred procedure, the required differential pressure is compared to the available differential pressure. If there is not sufficient differential pressure available, either the suction pump is turned on or the engine operating state is altered. In the case of a change in the operating state, such a state, accompanied by elevated intake-manifold vacuum pressure, is adjusted in that the engine control reduces the throttle-valve opening.

[0017] In a further refinement of the inventive idea, an additional throttling takes place in stratified operation. In the case of catalyst heating using a retarded ignition timing, an ignition timing that is optimal for efficiency is given priority over the catalytic converter heating. As a result, the engine requires less air-mass flow, the throttle valve may be closed, and the intake-manifold pressure decreases.

[0018] The changes in the operating state having elevated intake-manifold vacuum pressure may be made furthermore by intervening in the power efficiency specifications or in the operating state specifications of the engine management. In the case of engine management, direct interventions in the ignition timing are also conceivable without necessitating computational modeling of the efficiency or the operating state.

[0019] In engine management concepts for optimizing consumption and exhaust-emission behavior, operating states associated with high intake-manifold pressure occur. To respond to insufficient vacuum pressure in the servo system, the proposed method provides for either turning on the suction pump and/or altering the operating state to ensure sufficient vacuum pressure in the servo system. In this context, the proposed method eliminates the need, in particular, for the pressure sensor at the vacuum reservoir or, given the existence of a pressure sensor, eliminates the need for monitoring the sensor for correct functioning.

[0020] Another preferred procedure of the method according to the present invention provides for the quantity flows fed to the vacuum reservoir and/or the quantity flows removed from the vacuum reservoir to be continually summed using the appropriate operational sign, or integrated. The contents of the vacuum reservoir are thus able to be continually and dynamically adapted to the quantity flows existing at any one time and, on the basis of the contents, the pressure prevailing in the reservoir may be predicted at any point in time. In this connection, the quantity flows in question may either be summed as discrete air volumes or be integrated as infinitesimal air-volume variations.

[0021] The method according to the present invention may additionally provide that flow quantities only be removed from the vacuum reservoir when the difference between the pressure prevailing in the intake manifold or suction pump and the pressure prevailing in the vacuum reservoir exceeds a predefined threshold value. In reality, technically speaking, between the vacuum reservoir and the intake manifold, at least a non-return valve is installed, which is likewise considered on the basis of the proposed threshold value in the model calculation according to the present invention. In this context, the threshold value may be adapted to the particular physical conditions and, thus, be used as an additional parameter for optimizing the proposed model. Moreover, pressure losses possibly occurring due to flow resistance in the line may be considered on the basis of the parameter.

[0022] The model calculation underlying the present invention may also provide for calculating the quantity flows fed to the vacuum reservoir and/or the quantity flows removed from the vacuum reservoir from operating states of the internal combustion engine, in particular from driving states of the motor vehicle. On the one hand, the pressure prevailing in the intake manifold is dependent upon the operating states of the internal combustion engine, in so far as the air supplied by the intake manifold to the combustion chamber is dependent upon the current state of combustion, and, on the other hand, the air supplied to the intake manifold, for example via the throttle valve, is controllable. In the case of a motor vehicle, parameters such as vehicular speed or braking deceleration may be consulted. From these, inferences may then be made, in particular, with respect to the air masses supplied via a brake booster to the vacuum reservoir. In accordance with another advantageous embodiment of the method of the present invention, the quantity flows fed to the vacuum reservoir may be calculated using a step function that is triggered by a signal edge representing the servo function response. This proposed measure is consistent with the technical reality in so far as, in the case of a brake booster, for example, when a corresponding braking force is applied to the brake booster in response to a braking maneuver, the quantity flows fed to the vacuum reservoir correspond approximately to a step function having a more or less constant time duration per braking intervention. In this context, the proposed step function may be modeled, in particular, in the form of a monoflop.

[0023] Based on the modeling of the pressure in the vacuum reservoir proposed by the present invention, as a function of the pressure prevailing in the vacuum reservoir, as calculated from the balance of the flow quantities, it may also be provided for an intervention to be made in the internal combustion engine to lower the pressure in the vacuum reservoir, in particular, for a throttle valve, provided for instance in the intake manifold, to be adjusted, and/or for the suction pump to be turned on. As a result of this intervention, therefore, the vacuum pressure required for the servo system is again automatically made available in response to the exceeding of a pressure threshold, without the need for any intervention or interaction on the part of the driver. Thus, according to this embodiment, an appropriate vacuum pressure is assured at all times.

[0024] Alternatively or additionally thereto, as a function of the pressure prevailing in the vacuum reservoir, as calculated from the balance of flow quantities, an appropriate flag (indicator) may be set and, in particular, a control or warning signal may be output. Thus, in this exemplary embodiment, an intervention in the internal combustion engine is not necessarily automatically made to lower the pressure in the vacuum reservoir. Rather, an appropriate bit is initially set which is subsequently able to trip a corresponding control or warning signal. This enables the driver to initiate the necessary countermeasures on his/her own accord, or he/she is at least informed about the initiated measures.

[0025] In accordance with another preferred exemplary embodiment of the method according to the present invention, the calculated pressure prevailing in the vacuum reservoir may be used for monitoring a possibly provided pressure sensor for correct functioning. In this connection, the model-based calculation of the pressure prevailing in the vacuum reservoir is used as a further safety feature for an internal combustion engine of the species and, thus, makes it possible to detect a malfunction of an already existing pressure sensor.

[0026] It is emphasized here that, of the various servo functions provided in a motor vehicle—as far as maximum driving safety is concerned—the brake servo (booster) function is to be given precedence over the other servo functions. Thus, in accordance with one advantageous further refinement of the inventive idea, in the case of insufficient vacuum pressure in the vacuum reservoir, functions such as servo (power) steering or resonance throttle control may be temporarily deactivated, in order to at least ensure an adequate brake servo function. This is important, above all, when the user demands braking force to such a degree (for example by pumping the brake pedal) that even the electrical suction pump is not able to evacuate the air volume required for this quickly enough from the vacuum reservoir.

[0027] The assumption may also be made in a first advantageous approximation, when modeling the mass flows flowing into and out of the vacuum reservoir, that the sum of the inflowing and outflowing air flows is constant. Furthermore, in choosing the dimensions of the integrator/summator of the inflowing and outflowing mass flows, as a lower limit, one may assume the pressure prevailing in the intake manifold or in the suction pump and, as an upper limit, the ambient pressure.

[0028] The present invention is also directed to a computer program which is suited for implementing the above-described method when it is carried out on a computer. Especially preferred, in this context, is a computer program which is stored in a memory, in particular in a flash memory.

[0029] The control unit likewise proposed in accordance with the present invention for an internal combustion engine of the species includes means for detecting the actuation of at least one servo function, means for sensing the pressure prevailing in the intake manifold, means for sensing the operating state of the suction pump, and means for calculating the pressure prevailing in the vacuum reservoir, which provide for quantity flows to be fed to the vacuum reservoir when at least one servo function responds, and for quantity flows to be removed from the vacuum reservoir when the pressure prevailing in the intake manifold is less than the pressure prevailing in the vacuum reservoir, and which provide for the pressure prevailing in the vacuum reservoir to be calculated from the balance of flow quantities fed to and removed from the vacuum reservoir. Thus, first of all, data-acquisition means are provided, for example, a switch or a sensor for detecting the actuation of at least one servo function, for example, a stop-light or brake-light switch for detecting a brake actuation, as well as means for sensing the intake manifold pressure required for the model calculation, and the operating state of the suction pump. Means are provided, moreover, for processing this acquired information on the basis of the proposed model.

[0030] Further features and advantages of the method according to the present invention, as well as of the control unit, are derived from the following, on the basis of the exemplary embodiment of the present invention described on the basis of a drawing, whose individual figures show:

[0031]FIG. 1 a block diagram of a motor-vehicle internal combustion engine according to the present invention;

[0032]FIG. 2 a flow chart of a first section of an exemplary embodiment of a method according to the present invention;

[0033]FIG. 3 a flow chart of a second section of the method; and

[0034]FIG. 4 a flow chart of a third section of the method.

[0035] The internal combustion engine shown in FIG. 1 has an intake manifold 1, which is coupled via valves 2 (not shown more closely here) to a combustion chamber 3 of the internal combustion engine. Air is supplied to the intake manifold via an opening 4. Via a line 5, intake manifold communicates in a pressure-conductive manner with a vacuum reservoir 6. A non-return valve 7 is configured within this line path. Servo devices of the motor vehicle, which are installed in the existing internal combustion engine, communicate in particular, in pressure-conductive manner (via pressure-media lines) with vacuum reservoir 6. Provided as servo systems in the present exemplary embodiment are a brake booster 8, which communicates in a pressure-conductive manner via a master brake cylinder (not shown here) with a brake pedal 9, as well as a servo power steering system 10 and a resonance throttle control 11. The latter supplies the auxiliary power necessary for operating a resonance valve 12. These servo systems communicate in a pressure conductive manner via lines 13, 14, 15 with vacuum reservoir 6.

[0036] Also provided in pressure lines 13, 14, 15 are valves 16, 17, 18, by way of which, only as needed, the individual servo systems may be coupled in a pressure-conductive manner to the vacuum reservoir. Air flows in line 5 between intake manifold 1 and vacuum reservoir 6, in one of the two directions, depending on whether the pressure in the intake manifold is lower or higher than that in vacuum reservoir 6. The already mentioned non-return valve 7 assures, in particular, that the air flow is avoided in the direction of the vacuum reservoir, so that vacuum reservoir 6 is not flooded with air, as soon as a higher pressure prevails in intake manifold 1 than in vacuum reservoir 6.

[0037] Also provided in intake manifold 1, in the vicinity of opening 4, is a throttle valve 19, which is used controlling and/or regulating of air flow 4 a flowing into the intake manifold. Additional bypass line 20 makes it possible to ensure that sufficient air is supplied to the intake manifold during idle operation of the internal combustion engine. In this context, bypass line 20 is controlled in open and/or closed loop via an idle actuator 21.

[0038] Also provided on the intake manifold is a pressure sensor 22 for measuring the pressure prevailing in the intake manifold. The signal supplied from pressure sensor 22 may first be fed to an intake-manifold pressure sensor electronics 23 or, however, be directly transmitted to an electronic control unit 24.

[0039] In comparable fashion, the output signal from idle actuator 21 is fed to electronic control unit 24. In addition, the position of throttle valve 19 is determined via a throttle-valve potentiometer 25, and the corresponding measurement signal is likewise fed to electronic control unit 24.

[0040] As further pressure information, the pressure prevailing in vacuum reservoir 6 is supplied, first of all, by a pressure sensor 26, via a possibly existing pressure-sensor electronics 27, to control unit 24. The ambient pressure required for the computational model according to the present invention (see FIGS. 2 through 4) is ultimately communicated by an ambient-pressure sensor 28 to control unit 24.

[0041] Vacuum reservoir 6 is coupled in fluid communication via a line 29 to a suction pump 30, which, in turn, is driven via a line 31 by control unit 24 and transmits signals indicative of its operating state to this control unit.

[0042]FIGS. 2 through 4 show a method sequence, in accordance with which, the vacuum pressure prevailing in vacuum reservoir 6 is determined using an appropriate model. The flow chart illustrated in FIG. 2 relates to the ascertainment of the quantity flows removed from vacuum reservoir 6 and begins with a starting block 32. After that, the section of the method depicted in FIG. 2 subdivides into three branches A, B, and C.

[0043] In the left branch A in FIG. 2, the query is initially made in block 33 as to whether electrical suction pump 30 is turned on. When the pump is turned off, a value m_(ab1) for the air evacuated from vacuum reservoir 6 is set to zero in block 34.

[0044] If the pump is turned on, the difference A₁ between pressure P_(BKV) prevailing in vacuum reservoir 6 and the minimally attainable pressure P_(min) from electrical suction pump 30 is calculated in block 35. Pressure P_(BKV) prevailing in vacuum reservoir 6 is extracted from memory 36, in which the pressure calculated during a preceding loop and prevailing in vacuum reservoir 6 is stored. Pressure P_(min) that is minimally attainable from electrical suction pump 30 is calculated in block 37. There, a factor F₁ is applied to ambient pressure Pu supplied by ambient pressure sensor 28. This allows for the fact that electrical suction pump 30 is only able to provide a specific pressure difference in comparison with ambient pressure p_(U).

[0045] A value m_(ab1) for the air volume that is able to be evacuated by electrical suction pump 30 from vacuum reservoir 6 is calculated in block 38 by applying a factor F₂ to difference Δ₁. Factor F₂ is stored in a memory 39 and represents a weighting factor which may be used to allow for the influence of electrical suction pump 30 on the entire system.

[0046] In the right branch C of the flow chart in FIG. 2, the air volume, which may be evacuated into intake manifold 1 of the internal combustion engine, is calculated. For this, difference Δ₃ between pressure p_(S) prevailing in intake manifold 1 and pressure P_(BKV) prevailing in vacuum reservoir 6 is initially calculated in block 40. The pressure in intake manifold 1 is supplied by pressure sensor 22; pressure P_(BKV) in vacuum reservoir 6 is retrieved from memory 36, as already described above with respect to left branch A. In block 41, a weighting factor F₃, which is stored in a memory 42 and through which the influence of intake manifold 1 on the entire system may be considered, is applied to difference Δ₃. The result of the operation performed in block 41 is a value m_(ab3) for the air volume evacuated from vacuum reservoir 6 into intake manifold 1.

[0047] In middle branch B, a value m_(ab2) is set to zero (block 43). The purpose of this measure is explained further below.

[0048] From the three values m_(ab1), m_(ab2) and m_(ab3), the minimal value is generated in block 44. Under normal circumstances, i.e., when minimally attainable pressure P_(min) from electrical suction pump 30 and/or pressure p_(S) in intake manifold 1 are lower than pressure P_(BKV) in vacuum reservoir 6, then values m_(ab1) and m_(ab3), respectively, are negative values. In rare cases, it can occur, however, that pressure P_(BKV) is less than pressure ps prevailing in intake manifold 1 or than pressure P_(min) that is attainable by electrical suction pump 30. This can be the case, for example, during uphill travel of a motor vehicle, when the vehicle has to overcome a substantial altitude difference. In such a case, air would flow into vacuum reservoir 6 and “fill” it up again, which, of course, is undesirable and is prevented by non-return valve 7. The influence of the non-return valve in such a case is taken into account in that, in block 43, a value m_(ab2) is set to zero, which, in this rare case, is used as a minimal value in block 44.

[0049] A second section of the method for operating vacuum reservoir 6 is shown in FIG. 3, in which the supplied quantity flows of the model are ascertained and which likewise begins with start block 32 and divides into two branches D and E. In left branch D in FIG. 3, it is queried in block 45 whether brake booster 8 was actuated via brake pedal 9. In this context, an actuation is understood to be a dynamic process where the brake is brought from a released state into an actuated state. Remaining in the actuated stationary state would signify the query result “no” in decision block 45. In this case or in the case where the brake remains in a stationary, released state, a value for air volume m_(to1) flowing to vacuum reservoir 6 from brake booster 8 is set to equal zero. Alternatively, in block 47, air volume m_(to1) is calculated from the sum of two values m_(B) and m_(p), which are stored in memories 48 and 49. In this context, value m_(B) stands for that air volume which flows from brake booster 8 into vacuum reservoir 6 in response to a dynamic actuation of the brake. Value m_(p) takes into account that, during a braking operation, the brake power often changes, so that additional air flows from brake booster 8 into vacuum reservoir 6. Such a process is also described as “pumping”.

[0050] In the right branch E of the flow chart in FIG. 3, it is queried in block 50 whether the brake is released. Analogously to the explanations regarding block 45, here a releasing of the brake signifies that the brake passes dynamically from an actuated to a released state.

[0051] If the brake, i.e., brake pedal 9 and brake booster 8, remains in a stationary, released state, the response in decision block 50 is “no”. In this case, no air flows from brake booster 8 to vacuum reservoir 6. This is taken into account in block 51 in that an air volume m_(to2) is set to zero.

[0052] If the response in decision block 50 is “yes”, in block 52, air volume m_(to2) flowing to vacuum reservoir 6 is set to equal value m_(B) stored in memory 49.

[0053] From the values m_(to1) and m_(to2), the sum m_(to3) is generated in block 53. To this is added, in block 54, a value M_(L) which is stored in a memory 55. The thus calculated value m_(to4) takes into account a base leakage, corresponding to value M_(L), that is assumed for the system.

[0054] The air volume m_(to) ultimately flowing to vacuum reservoir 6 is calculated in block 56, in that a factor F₄ is applied to value m_(to4). This factor F₄ takes into account that air volume m_(to) flowing into vacuum reservoir 6 in response to a brake actuation by brake booster 8, and also base leakage m_(L), are dependent upon the pressure differential between ambient pressure P_(U) and pressure P_(BKV) prevailing in vacuum reservoir 6. Factor F₄ is calculated in block 57 on the basis of this pressure differential.

[0055] Reference is made at this point to the method section illustrated in FIG. 4, where a balancing of flow quantities is undertaken for the model:

[0056] In block 58, the difference is calculated between value m_(to) determined in FIG. 3 and value m_(ab) determined in FIG. 2, thus a balancing of flow quantities is undertaken using the appropriate operational signs. From this, taking into consideration the ideal gas equation and the volume of vacuum reservoir 6, pressure p_(BKV) prevailing in vacuum reservoir 6 is calculated in subsequent block 59, using continuous integration. This is compared in block 70 to a minimum value, namely to the intake manifold pressure during idle running of the internal combustion engine or to the minimum pressure of the electrical suction pump, and set to equal this value, provided that this minimum value is fallen short of (not met) due to the integration. Analogously hereto, a comparison to a maximum value, namely to the ambient pressure, is made in block 71, and the pressure in the vacuum reservoir is set to equal this maximum value, when this value is exceeded by the calculated value.

[0057] On the basis of this calculated pressure P_(BKV) stored in vacuum reservoir 6, it is now determined whether measures need to be introduced to lower pressure ps in intake manifold 1, or whether electrical suction pump 30 needs to be switched on. For this, value P_(BKV) in block 60 is compared to a limiting value P_(G1) which is stored in a limit value memory 61. A “yes” response in block 60 (thus, if there is not enough vacuum pressure in vacuum reservoir 6) prompts control unit 24 to switch on electrical suction pump 30 in block 62. An alarm signal may also be optionally output, e.g., a warning light lit up in the motor vehicle dashboard.

[0058] If the response in block 60 is “no”, which is synonymous with a pressure in vacuum reservoir 6 corresponding at least to desired setpoint p_(G1), it is checked in block 63 whether pressure p_(BKV) prevailing in vacuum reservoir 64 is less than a limiting value p_(G2) which is stored in a limit value memory 64. A “yes” response in block 63 prompts control unit 24 to switch off electrical suction pump 30 in block 65. In this context, limiting value p_(G2) is less than value p₁, in order to maintain a hysteresis among the conditions which justify switching electrical suction pump 30 on or off. The hysteresis prevents a “bouncing” (fluttering) of electrical suction pump 30, as on and off commands are output to electrical suction pump 30 in rapid succession.

[0059] If the suction capacity of electrical suction pump 30 does not suffice to establish the required pressure p_(G1) in vacuum reservoir 6 within a specific time period, this is determined in block 66 and, if indicated, a measure is introduced to lower the pressure in intake manifold 1. This includes, for example, adjusting throttle valve 19. If indicated, the outputting of an alarm may also be initiated. By placing block 66 behind block 62, priority is given to the switching on of electrical suction pump 30, over an engine intervention. This has the advantage, particularly when working with GDI engines and e-gas systems, that the engine is able to be operated in the optimal working range for low fuel consumption and low exhaust-gas emission.

[0060] The loop ends in block 67. From there, if indicated, a return to start block 32 may follow. In this context, the return may follow, for example, cyclically at a specific clock-pulse rate, or as an event-driven return. 

What is claimed is:
 1. A method for operating a vacuum reservoir (6) provided in an internal combustion engine, in particular of a motor vehicle, which supplies the auxiliary power, in the form of a vacuum pressure, needed for at least one servo unit (8, 10, 11), and which is acted upon by a vacuum pressure prevailing in an intake manifold (1) of the internal combustion engine and in an, in particular, electrical suction pump (30), wherein in a model, quantity flows are fed to the vacuum reservoir (6) when at least one servo unit (8, 10, 11) is actuated; quantity flows are removed from the vacuum reservoir (6) when the pressure prevailing in the intake manifold (1) is lower than the pressure prevailing in the vacuum reservoir (6); quantity flows are removed from the vacuum reservoir (6) when the electrical suction pump (30) is switched on; and the pressure prevailing in the vacuum reservoir (6) is determined from the balance of the flow quantities fed to and removed from the vacuum reservoir (6).
 2. The method as recited in claim 1, wherein the quantity flows (56) fed to the vacuum reservoir (6) and/or the quantity flows (44) removed from the vacuum reservoir (6) are continually summed using the appropriate operational sign, or integrated (58).
 3. The method as recited in claim 1 or 2, wherein the flow quantities are only removed from the vacuum reservoir (6) when the difference between the pressure prevailing in the intake manifold and the pressure prevailing in the vacuum reservoir (6) exceeds a predefined threshold value.
 4. The method as recited in one or more of the claims 1 through 3, wherein the quantity flows (44) fed to the vacuum reservoir (6) and/or the quantity flows (44) removed from the vacuum reservoir (6) are determined from operating states of the internal combustion engine, in particular from driving states of the motor vehicle.
 5. The method as recited in one or more of the preceding claims, wherein the quantity flows (56) fed to the vacuum reservoir (6) are determined using a step function that is triggered by a signal edge representing a servo unit (8, 10, 11) response.
 6. The method as recited in one of the preceding claims, wherein as a function of the pressure prevailing in the vacuum reservoir (6), as calculated from the balance of the flow quantities, an intervention is made in the internal combustion engine to lower the pressure in the vacuum reservoir (6), in particular, the suction pump (30) is turned on, and/or a throttle valve (19), provided for instance in the intake manifold (1), is adjusted.
 7. The method as recited in claim 6, wherein priority is given to the switching on of the suction pump (30), over an engine intervention.
 8. The method as recited in one or more of the preceding claims, wherein the calculated pressure prevailing in the vacuum reservoir (6) is used for monitoring a possibly provided pressure sensor (27) for correct functioning.
 9. A computer program wherein it is suited for implementing the method according to one of claims 1 through 8 when it is executed on a computer.
 10. The computer program as recited in claim 9, wherein it is stored on a memory, in particular on a flash memory.
 11. A control unit for an internal combustion engine, in particular of a motor vehicle, in which a vacuum reservoir (6) is provided, which supplies the auxiliary power, in the form of a vacuum pressure, needed for at least one servo function (8, 10, 11) of the internal combustion engine, and which is acted upon by a vacuum pressure provided by an intake manifold (1) of the internal combustion engine and by a suction pump (30), characterized by means (9, 61) for detecting the actuation of at least one servo function (8, 10, 11); means (23) for sensing the pressure prevailing in the intake manifold (1); means for detecting the operating state of the suction pump (30); and means for determining the pressure prevailing in the vacuum reservoir (6), which provide that quantity flows are fed to the vacuum reservoir (6) when at least one servo function (8, 10, 11) responds; and quantity flows are removed from the vacuum reservoir (6) when the pressure prevailing in the intake manifold (1) is lower than the pressure prevailing in the vacuum reservoir (6); quantity flows are removed from the vacuum reservoir (6) when the suction pump (30) is switched on; and which provide that the pressure prevailing in the vacuum reservoir (6) is determined from the balance of the flow quantities fed to and removed from the vacuum reservoir (6).
 12. The control unit as recited in claim 11, characterized by a summator or integrator (58), which continually sums or integrates the quantity flows fed to the vacuum reservoir (6) and/or the quantity flows removed from the vacuum reservoir (6).
 13. The control unit as recited in claim 11 or 12, characterized by means for detecting a signal edge representing the response of a servo function (8, 10, 11), and by means for calculating the quantity flows fed to the vacuum reservoir (6), on the basis of a step function.
 14. The control unit as recited in one or more of the claims 11 through 13, characterized by means (12, 19, 20) for switching on the suction pump (30) and/or for making an intervention in the internal combustion engine to lower the pressure in the vacuum reservoir (6), in particular, for adjusting a throttle valve (19), provided for instance in the intake manifold (1), as a function of the pressure prevailing in the vacuum reservoir (6), as calculated from the balance of the flow quantities.
 15. The control unit as recited in one or more of the claims 11 through 14, characterized by means for monitoring a possibly provided pressure sensor for correct functioning, on the basis of the calculated pressure prevailing in the vacuum reservoir (6). 